Generally, an image processing system that uses a scanner or like apparatus for reading a document and storing it in the form of image data includes a function to analyze generated data and to automatically erase any image data generated from a blank document. However, if the document is, for example, a sheet of thin paper with content printed only on the front side thereof, a phenomenon known as “show-through” can occur in which the content printed on the front side of the document shows through to the back side, which can lead to the possibility of erroneously determining that the image data generated from the back side is not that of a blank document.
Generally, an image processing system that uses a scanner or like apparatus is also equipped with a function to analyze generated data and to correct any show-through portion of the image data. To correct the show-through portion properly, the position of the show-through portion of the image data must be accurately detected.
An image forming apparatus is disclosed that outputs a front-side image and back-side image of a two-sided document in the form of image data representing image densities. This image forming apparatus converts the pixel data of the back-side image so that the back-side image data generated by reading the side opposite to the front-side image data can be matched with the front-side image data, generates binarized back-side image data by binarizing the converted pixel data, and obtains overlapping image data by ANDing the binarized back-side image data with the front-side image data. Then, the image forming apparatus applies thresholding to the overlapping image data to produce image data from which components due to the show-through of the back-side image have been excluded, and obtains image data corresponding to all the pixels contained in the front-side image by combining the thresholded image data with image data produced by subtracting the overlapping image data from the front-side image data (see Japanese Laid-open Patent Publication No. H06-62216).